Recreational vehicles, motor homes, trucks, boats and the like, particularly ones of the larger variety, often have a plurality of water and coolant circuits. A first circuit may extend from the engine of the vehicle or boat and is typically used for heating the interior or the vehicle or boat. A second circuit may extend from an auxiliary heater which may also be used for heating when the engine is not operating. A third circuit may extend from a source of potable water used for cooking and other personal use. A further circuit may be used for zone heating and heat exchangers between the various circuits are common. The heating module and the engine are usually not made by the same manufacturer and they may not be installed at the same time. Accordingly, adapting a the previously installed system with a newly installed system is inefficient and time consuming due to the many connections, heat exchanger, pumps valves and the like.